In the field of high speed printers, the drum printer has proved to be very successful in providing a rotating surface against which print hammers impact the characters carried on such surface. However, the need for a reduction in weight along with compactness in size and decrease in cost has brought about the endless print band or belt which carries integral type characters in a line along the print station and past the print hammers. Such print hammers are constructed in a bank which includes hammer drive solenoids for causing the hammers to be driven against the type characters on the band in a sequence dictated by the desired printing program.
The print band is trained around a drive pulley and a driven or idler pulley normally in a horizontal manner, such pulleys being crowned to provide a tracking surface for the band. Provisions may also be made in the supporting structure for the pulleys to permit rapid changing of print bands while at the same time maintaining proper tension on the band during operation.
Various ways and means have been utilized in the past for maintaining a print belt, chain, band, or the like in a precise path past the print station so as to prevent the type characters thereon from moving in vertical displacement from the line of print hammers.
Representative prior art relating to the subject matters of the present invention is disclosed in U.S. Pat. No. 3,012,499, as issued on Dec. 12, 1961 to S. Amada, wherein a high speed printing system has a type belt with printing type thereon and a guide is provided with upper and lower portions to fit over the edges of the belt for suppressing vibration and shifting of the type belt and a central portion is provided to receive the force of the printing type.
U.S. Pat. No. 3,216,348, issued on Nov. 9, 1965 to K. F. Oldenburg et al., discloses hammer timing means in a high speed belt printer having a belt with hammers and a sprocket for driving the belt. The belt is guided along a channel shaped guideway and includes flanges which overlap the edges of the belt so as to maintain such belt in contact with the guideway as it is advanced past the hammers.
U.S. Pat. No. 3,224,366, issued on Dec. 21, 1965 to J. M. Cunningham, discloses a type carrier device which includes a stationary guide member taking the form of a monorail attached to a support plate and having parallel spaced-apart straight portions connected at opposite ends by curved portions to form a continuous closed guide path for the type elements.
U.S. Pat. No. 3,402,657, which issued on Sept. 24, 1968 to J. T. Potter et al., discloses a high speed belt printer with printing slug supporting means wherein a print chain is established by a plurality of integrally casted printing slugs clipped about the edges of an elastic timing belt. The print chain is supported relative to the print hammers by a frame featuring a modular or sub-assembly construction in which the basic components are formed from a length of precision stock of the same cross-section.
U.S. Pat. No. 3,745,918, which issued on July 17, 1973 to F. J. Perry et al., discloses U-shaped type carriers with legs of increasing width which overlap the legs of adjacent carriers to provide stability and close spacing of the type characters, and provides for upper and lower guide members having inturned lip portions which engage each type carrier to maintain same in operating alignment along a printing line.
U. S. Pat. No. 3,805,697, issued on Apr. 23, 1974 to J. A. Mahe, discloses a cartridge for a print character band which includes a pair of magnetic strips to maintain the print band against a portion of the inner wall of the cartridge cover.
U.S. Pat. No. 3,805,698, issued on Apr. 23, 1974 to G. W. Bowers, Jr. et al., discloses a print carrier and transport cartridge which has an endless print band or belt with guide means formed by a V-shaped ridge around the belt. The cartridge includes a housing having a side wall which includes a recessed portion that cooperates with the ridge of the print bet as it passes the hammer assembly, thereby restraining the print characters from moving in an upward or downward direction.
U.S. Pat. No. 3,972,282, issued on Aug. 3, 1976 to J. Konkel, discloses a type train assembly having a pair of endless belts, type carriers with type blocks, and a guide mounted on a support with the guide having a slot for the blocks. A carrier guide bar is also mounted on the support to hold the type blocks in position and to provide rigid support for the type faces when struck by the hammers.
And U.S. Pat. No. 3,630,144, which issued on Dec. 28, 1971 to F. Hilpert et al., discloses a toothed belt with type carriers thereon maintained along a print line by means of a C-shaped type carrier guide within the printer station and opposite the printer hammers provided.